There are numerous known power assist steering systems that provide additional steering torque when needed. These include conventional hydraulic steering systems, electric power assist hydraulic steering systems as well as electric power steering systems that include no hydraulics. Typically, an electric power steering system includes an electric motor coupled to an electric control unit responsive to movement of a hand steering wheel under preselected vehicle conditions. The electric motor, when activated, supplies an auxiliary steering force to a rack member to assist the driver during a steering maneuver. In general, an auxiliary steering force is desired at relatively low vehicle speeds such as during vehicle parking, especially when a relatively high torque is applied at the hand steering wheel.
Conventional electric steering systems have high power demands when operated, which often cause excessive strain on the vehicle electrical system. At lower vehicle speeds the vehicle alternator operates more slowly and, therefore, may not be able to supply sufficient power to both the vehicle loads and the electric steering system. The substantial power requirements of such electric power steering systems may lead to an undesirable operation of other vehicle electrical loads, such as dimming lights and slow operating wipers. Proposed solutions to address the additional drain on the vehicle electrical system have not been completely satisfactory, as they often require complicated generator structures, expensive components, and/or complex control equipment.